FEASIBILITY STUDY OFSTAND-ALONE SMALL-SCALE DIGESTION SYSTEMSTO PRODUCE BIOGAS FOR LOCAL USE

FEASIBILITY STUDY OF STAND-ALONE SMALL-SCALE DIGESTION SYSTEMS TO PRODUCE BIOGAS FOR LOCAL USE

MARIE JANET EUSTASIE

Master of Science Thesis

Stockholm, Sweden Year 2012

FEASIBILITY STUDY OF STAND-ALONE SMALL-SCALE DIGESTION SYSTEMS TO PRODUCE BIOGAS FOR LOCAL

USE

MARIE JANET EUSTASIE

MSc Thesis Year 2012

Department of Energy Technology Division of Heat and Power Technology

Royal Institute of Technology

Master of Science Thesis, EGI 2012: 042MSC EKV891

Feasibility study of stand-alone small-scale digestion systems to produce biogas for local use

Marie Janet Eustasie

Approved Examiner

Prof. Professor Torsten H. Fransson

Supervisor

Dr. Anders Malmquist Commissioner

Prof. Professor Torsten H. Fransson

Contact person Dr. Anders Malmquist

ABSTRACT

The purpose of this project was to carry out a feasibility study of implementing a small-scale biogas plant on KTH campus using food wastes from the neighbouring restaurants and KTH kitchens as input substrate, where the biogas produced could be used in the Energy laboratory, to run the micro turbine, as an example. Considering that KTH has 10 departments and that each department has its own kitchen, the amount of food wastes that can be recuperated for input to the plant is around 225 kg per day for a normal working week, requiring a 10m ³ biogas plant.

This report also relates to the potential implementation of small-scale biogas plants on farms in Mauritius using manure and crop endings as input substrate as a solution to the waste management problems the farmers are currently facing as well as using the biogas to provide energy for cooking and heating.

Based on the quantity of food wastes available from the neighbouring restaurants, the sizing of the proposed biogas plant was calculated and the best technical and commercial options were considered.

An experimental biogas plant was setup on the campus and the planning and logistics involved were studied as well as the potential quantity and quality of gas produced from food wastes. The optimal biogas production for a 5 m ³ capacity biogas plant and processing food wastes is 6 to 10 m ³ of biogas per day composed of about 68-72% methane. But, since the experiment was run for only a two-week period, the optimum biogas production could not be reached. Several operational and biological problems were encountered during the operation of the plant. However, the output of the experiment is positive as the logistics required for the setting up and running of a biogas plant on campus or elsewhere including the technicality of such a plant and the human resources requirements have been deduced from the lessons learned.

Keywords : Anaerobic digestion, Food wastes, Manure, Mauritius, Biogas, Small scale plants

ACKNOWLEDGEMENTS

I would like to express my greatest gratitude to the Assoc. Prof. Andrew Martin, SEE Worldwide Program Director and Prof Torsten Fransson, Chair, Heat and Power Technology, KTH as well as Dr Dinesh Surroop, Local Supervisor, University of Mauritius and Prof Roumila Mohee, Dean of the faculty of Engineering, University of Mauritius for believing in me and giving me this extraordinary opportunity to complete my Master’s thesis at the distinguished university of KTH.

I would also like to acknowledge and thank Dr Anders Malmquist, Deputy Project Manager, and Supervisor at KTH for his helpful discussions, advice and support during the execution of this work. I appreciate his time and support in directing me towards my goals.

I would not have gone through this enriching journey if not for Mr Tord Magnusson, who sponsored this scholarship to whom I owe my appreciation for this once-in-a-lifetime experience.

The project has obtained its financial support from InnoEnergy and the Division of Heat and Power at KTH through their Lighthouse Project Explore Polygeneration. This project made it possible to bring the test unit to KTH and to perform real biogas production tests through the experimental setup.

Next, I would like to extend my sincere thanks to Mr. Göran Holmberg, Akademiska hus, Mr. Claes Henningsson, CAMPUS AB who have helped me in acquiring the necessary resources for the setup of the experimental biogas plant on LTH grounds as well as Prof. Anna Schnürer, Dept. of Microbiology, Swedish University of Agricultural Sciences, Uppsala for her precious help in the understanding of the

‘microbiological process’ in the experimental setup.

The Livestock division of the Agricultural Research and Extension Unit (AREU), Mauritius has been very helpful in supplying the needful data for the basis of my project for which I am truly grateful.

Mr Gustav Rogstrand, Researcher, JTI Swedish Institute of Agricultural and Environmental Engineering and his team have helped me a lot in the setup and operation of the experimental biogas plant.

My thanks also go to Mr Jeevan Jayasuriya, Lecturer at the Heat & Power division at KTH who played a leading role in expanding the Distance based Sustainability Energy Engineering (DSEE) Programme to Mauritius and giving us a golden opportunity to follow the Sustainable Energy based Master programme KTH.

Throughout my life my parents, my brothers Francois and Jerry, and my sister Shirley have always played an important role in supporting me. Through these past months, they also encouraged and supported me with kindness and I thank them tenderly.

In closing, I would like to thank Erwin for his support, encouragement and patience during this period.

TABLE OF CONTENTS

ABSTRACT ... II ACKNOWLEDGEMENTS ... III TABLE OF CONTENTS ... IV LIST OF FIGURES ... V LIST OF TABLES ... VI NOMENCLATURE ... VII

1 INTRODUCTION ... 1

1.1 BIOGAS ... 1

1.2 THE BIOGAS PROCESS ... 1

1.3 BIOGAS PRODUCTION AT KTH ... 2

1.4 BIOGAS IN MAURITIUS ... 2

2 OBJECTIVES ...3

3 METHOD OF ATTACK ...4

4 LITERATURE REVIEW ...5

4.1 PRINCIPLES OF BIOGAS TECHNOLOGY ... 5

4.2 FACTORS AFFECTING THE ANAEROBIC DIGESTION PROCESS ... 5

4.3 ANAEROBIC DIGESTION SYSTEMS ... 8

4.4 PRE-TREATMENT STEPS ... 9

4.5 BENEFITS OF BIOGAS ... 10

4.6 POTENTIAL ENERGY USES OF BIOGAS ... 10

4.7 THE DIGESTED RESIDUAL PRODUCT (BIO-MANURE) ... 11

4.8 HOW BIOGAS IS USED IN MAURITIUS AT PRESENT ... 12

5 EXPERIMENT SETUP ... 13

5.1 AIM OF THE EXPERIMENT ... 13

5.2 AMOUNT OF WASTES TO BE DIGESTED ... 13

5.3 DESIGN AND SIZING OF THE BIOGAS PLANT ... 13

5.4 CHOICE OF BIOGAS PLANT AND JUSTIFICATIONS ... 19

5.5 LOGISTICS: PLANNING THE BIOGAS PLANT ... 19

5.6 EQUIPMENT SETUP ... 21

5.7 RESULTS AND DISCUSSIONS ... 24

5.8 LESSONS LEARNED AND FUTURE WORKS ... 29

5.9 MEASURES TO IMPROVE PROCESS ENERGY EFFICIENCY ... 32

6 PRODUCTION POTENTIAL OF BIOGAS (HEAT & POWER) FROM FARMS IN MAURITIUS ... 34

6.1 ESTIMATE OF CATTLE, PIG AND POULTRY MANURE... 34

6.2 BIOGAS PRODUCTION POTENTIAL ... 37

6.3 POWER PRODUCTION POTENTIAL ... 37

7 BIOGAS PRODUCTION TECHNOLOGIES ... 39

7.1 PRE-FEASIBILITY STUDY ... 39

7.2 TYPES OF DIGESTERS AVAILABLE ... 39

7.3 SUITABLE TECHNOLOGY FOR FARMS IN MAURITIUS ... 41

7.4 APPLICATIONS OF BIOGAS IN MAURITIUS ... 42

8 ECOMOMIC ANALYSIS ... 43

9 POLICY AND LEGAL FRAMEWORK ... 44

10 CONCLUSIONS ... 46

11 LESSONS LEARNED AND FUTURE WORK ... 47

12 REFERENCES... 48

LIST OF FIGURES

Figure 1.1: The General Anaerobic Digestion Process (adapted from http://www.anaerobic- digesters.com)

Figure 4.1: Simplified anaerobic digestion of organic matter [Gujer, W., and Zehnder, A. J. B., 1983]

Figure 4.2: General scheme of a common biogas plant with continuously stirred tank reactor (CSTR) in Europe [Institut für Energetik und Umwelt et al., 2006]

Figure 4.3: Benefits of Biogas from the anaerobic digestion of organic wastes Figure 4.4: Potential uses of biogas and digestate from anaerobic digestion

Figure 4.5: Slurry tanker, Schouten, New Zealand (http://www.schoutenmachines.co.nz)

Figure 5.1: Philippine BioDigester by: Gerardo P. Baron, December 2004, (Tarlac City, Philippines) [http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm]

Figure 5.2: Completed PE digester prior to final installation of lid and wrapping with insulation [http://biorealis.com]

Figure 5.3: Small and medium scale digester biogas plants, by BioTech, India [http://www.biotech- india.org]

Figure 5.4: Containerised biogas plant by BioBowser, Australia [http://www.srela.com.au/biobowser.php]

Figure 5.5: Components of the BioBowser containerised biogas plant [http://www.srela.com.au/biobowser.php]

Figure 5.6: The Research biogas production unit at JTI, Swedish Institute of Agricultural and Environmental Engineering

Figure 5.7: Proposed site for the biogas plant setup

Figure 5.8 : Main components of the mobile biogas plant ( Source: JTI) Figure 5.9: Disperator® grinder

Figure 5.10 : Amount of biogas produced as a percentage of gas storage bag volume Figure 5.11 : Amount of biogas produced 16 ^th June 2012 to 21 ^st June 2012

Figure 5.12 : % of Methane in the biogas produced

Figure 5.13 : Percentage of carbon dioxide in the biogas produced Figure 5.14 : Percentage of oxygen in the biogas produced Figure 5.15: Upgrading of biogas (IEA Bioenergy, 2006)

Figure 6.1: Number of cattle, goats, sheep and pigs by type of breeder as at June 2011, Mauritius [AREU, 2011]

Figure 6.2: Location of clusters of small scale poultry farms in Mauritius [AREU, 2011]

Figure 7.1: Horizontal Digester [T. Fischer & A. Krieg, 2002]

Figure 7.2: Standard Digester in Agriculture [T. Fischer & A. Krieg, 2002]

Figure 7.3: Upright Large Digester [http://www.biotech-india.org]

Figure 7.4: Geo-membrane biogas plant [http://www.biotech-india.org]

LIST OF TABLES

Table 4.1: Theoretical biogas and methane production from carbohydrates, fats and proteins [Buswell

&Neave, 1930]

Table 4.2: Average characteristics of different manures and their biological methane potentials (BMP) [1) Viljavuuspalvelu, 2004; 2) Steineck et al., 1999; 3) KTBL, 2010; 4) Ministerium für Ernährung, Landwirtschaft, Forsten und Fischerei Mecklenburg-Vorpommern, 2004; 5) Institut für

Energetik und Umwelt et al.,2006; 6) Edström, 2011]

Table 5.1: Survey of restaurant wastes

Table 5.2: Mobile biogas plant basic data (Source: JTI) Table 5.3: Operation of the biogas plant

Table 5.4: Results of analysis of feed substrate (sample taken on the 13 ^th June 2012)

Table 5.5: Results of analysis of digestate samples at the beginning and at the end of the experiment Table 6.1: Number of breeders and livestock/ poultry status by geographical district as at June 2011

[AREU, 2011]

Table 6.2: Standard live-weight values of animal husbandry [Werner U., Stohr U., Hees N., 1989]

Table 6.3: Biogas production from different feedstock

Table 6.4: Average production potential of biogas power and heat in Mauritius from farm manure.

NOMENCLATURE Subscripts

N tot Total Nitrogen Abbreviations

°C degrees Celcius

A Amperes

AREU Agricultural Research and Extension Unit BMP Biological Methane Potentials

CH4 methane

CHP Combined Heat & Power

DIY Do-It-Yourself

DM Dry Matter

DMC Dry Matter Content

EC European Community

EUR Euro

GEF Global Environment Facility

GHG Green House Gas

Gkg Giga kilogram

Gm ³ Giga cubic metres

GWh Giga Watt Hour

h/d hours/ day

HRT Hydraulic Retention Time hr or h hour

IPP Independent Power Producers

JTI Swedish Institute of Agricultural and Environmental Engineering KTH Kungsliga Tekniska Hogskolan (Royal Institute of Technology)

kg Kilogram

kW Kilowatts

kWh Kilo Watt Hour

LPG Liquefied Petroleum Gas m ³ /t cubic metres per tonne

MID Maurice Ile Durable (Mauritius Renewable Island)

min minutes

MW Mega Watt

Nm ³ Normal Cubic Metres

No. Number

OLR Organic Loading Rate

PLC Programmable Logic Controller

PN Pressure Number

PPE Personal Protective Equipment Prof. Professor

Ref. Reference

TS Total Solids

tFM tonnes of Fresh Matter tVS tonnes of Volatile Solids

UNDP United Nations Development Programme

VS Volatile Solids

1 INTRODUCTION

This project has been chosen to be able to demonstrate the feasibility of the implementation of a small-scale anaerobic digester at KTH using food-wastes from KTH kitchens and neighbouring restaurants as substrate and using the biogas produced in the energy laboratory. This project will also cover the feasibility of implementing small-farm-scale anaerobic digesters as a means of farm waste management as well as a source of renewable and carbon free energy in terms of biogas in Mauritius.

The anaerobic digestion of biomass to produce biogas is said to be a model in choosing the best alternative sources of energy for rural areas using the reasoning that it is cheap and it can be locally produced and used. Also, the biogas produced can be used for a number of purposes such as heating, lighting, fuel for cooking, local or on-the-grid electric power generation.

1.1 BIOGAS

Raw biogas is a colourless mixture of methane (60-70%), carbon dioxide (20-30%), and trace amounts of hydrogen sulphide depending on the conditions of production and on the origin of the input substrates. The biogas produced is usually saturated with water vapour.

1.2 THE BIOGAS PROCESS

Biogas is generated when organic material (manure, food wastes, yard wastes, sludge from sewage treatment plants, slaughterhouse waste, crop residues, etc.) is decomposed by micro-organisms in anaerobic (i.e. oxygen-free) conditions. Biogas is also produced in natural environments where the availability of oxygen is limited, such as in swamplands and in the stomachs of ruminants. Anaerobic decomposition also takes place in landfills and different types of biogas plants. The remaining residue, digestate, contains plant nutrients such as nitrogen, phosphorus and potassium, preserved from the substrates used and is a very good natural fertilizer which can be used in agriculture.

Figure 1.1: The General Anaerobic Digestion Process (adapted from http://www.anaerobic- digesters.com)

This biogas can be used as it is for cooking, heating or it can be upgraded (pressurised and removal of

CO 2 and H 2 S) and used to provide electricity or used as vehicle fuel.

1.3 BIOGAS PRODUCTION AT KTH

In line with the plan of developing the polygeneration mobile and flexible energy conversion unit that can function during extreme conditions, the small-scale biogas plant would be studied as an option for energy production. The biogas produced in the biogas plant would be used to test equipment such as the micro turbine in the energy laboratory.

Also, it must be noted that it is just a matter of time for Swedish regulations to impose the segregation of organic wastes in institutions such as schools, restaurants, hospitals, etc as well as at home.

This project will also open the opportunities for future collaboration of KTH to other stakeholders in the biogas production field

1.4 BIOGAS IN MAURITIUS

The importance of energy in the development of Mauritius as a Small Island cannot be over- emphasized. Energy represents a hub around which the island’s industrialisation and development revolves. Any change in the energy supply chain in time results into serious economic and social crunch. The role that energy plays in the production sustainability of industrial activities and in the elevation of the standard of living of the people is significant [Sambo, A. S. 2005].

The introduction of farm-scale anaerobic digesters for the production of biogas from manure is a perfect fit to the Maurice Ile Durable (MID) or Mauritius Sustainable Island project. One of the thrusts of the project is to make Mauritius less energy dependent on fossil fuels with a target autonomy of 65% by 2028, or a target 20% of our energy need from such renewable energy by 2025 through increased renewable energy use and the efficient use of energy in general [Ministry of Public Utilities Mauritius, 2008].

There exists at present a considerable number of small-scale to medium-scale poultry and pig farms as well as an increasing number of cattle farms in Mauritius. There are serious disposal problems and environmental pollution arising from the significant quantities of manure from these farms.

Furthermore, the biogas potential from this sector would be 16 GWh/year (Table 5.4).

The current waste management practices consist of letting the manure dry and used as natural fertilizer or further composted to be used as soil conditioner.

Therefore, there is a need to promote the biogas technology in Mauritius considering the large populations of poultry, pig and cattle farms and the related agricultural activities. This technology would provide an effective use of the farm manure and effluents and also reduce the environmental pollution caused by the disposal of manure.

Furthermore, these stand-alone remote systems can be engineered to meet the client demand without being connected to the grid. Often, farms in Mauritius are located in remote and inaccessible areas the extension to the electricity grid is not a cost effective solution and sometimes not technically possible.

Therefore, these systems are most promising for the energy production in such cases.

We should not forget to point out that although the potential for generating biogas energy from wastes in Mauritius is substantial, due to the Solid waste management policies in place in Mauritius, it is important to maintain a good coordination with the concerned authorities and corresponding policies.

Integrated farming is currently being exploited in Mauritius and the benefits will be able to bring a solution to the energy issues at the local level and probably as part of distributed energy systems. The magnitude if biogas production from animal waste will be quantified for more comprehensive analysis in this report.

Further in this report, I will also introduce the two cases where biogas is recovered and used as energy

in Mauritius at present. These two cases are at the St Martin wastewater treatment plant and at the

Mare Chicose landfill.

2 OBJECTIVES

This project is aimed at the following as it major objectives:

 Demonstrate how we can use low-cost technology digesters and bring engineering to it to improve its efficiency so that it can be affordable and easily sustainable by the users.

 The interest of my project is to study the possibility of producing biogas from kitchen and restaurant wastes from KTH to be used in the Energy Engineering Laboratory

 Also, to relate this experiment to the possibility of treating farm and crop wastes from small farms in Mauritius to produce biogas to be locally consumed for cooking and heating

 To create awareness among farmers in Mauritius related to the potential of generating biogas from

farm wastes and also generating a bio-fertiliser.

3 METHOD OF ATTACK

Initially, a work plan to schedule the project work was implemented.

According to the work plan, the background research work of the anaerobic digestion process including the literature review and consultations with local biogas producers and equipment suppliers was undertaken.

A comparison of the different available technologies was studied and the best option for the farm-scale digester in the Mauritian context is to be chosen.

Apply engineering knowledge to the proposed digester to improve the efficiency and to get a better quality of biogas produced.

Study of the different legal regulations and permits required for the setting up of an anaerobic digester as well as the health and safety requirements prevailing locally and how it applies to the Mauritian context.

The setup of a digester on the KTH university grounds would allow:

a) Verification of compliance to existing legal and safety requirements a) Identification of source and amount of biomass available for testing

b) Determination of requirements/needs of biogas energy in the KTH Energy laboratory c) Preparation of a bill of materials required for the digester

If time permits, a simulation of the engineering and energy controls on a low-technology digester would be carried out. First, familiarisation with the modelling software would be essential. Aspen V7.2 is the modelling platform base for the modelling of industrial and well as chemical processes. Creating a digester model and setting up control parameters are the main focal areas during familiarizing.

A economic analysis of the process for a farm- scale digester will be carried out, taking into account the re-use of the biogas for the process itself as well as any other indirect costs inferred, to be able to determine the most economical end uses of the biogas produced for a stand-alone system.

At the end, I will propose the way-forward and recommendations for further studies and produce a

report that addresses the targets.

4 LITERATURE REVIEW

4.1 PRINCIPLES OF BIOGAS TECHNOLOGY

The anaerobic digestion can be described as the biological degradation and stabilisation of biodegradable organic matter in specialised plants under controlled conditions. It is based on the formation of methane-rich gas and a nutrient –rich digestate through the microbial activity in oxygen free conditions. The anaerobic degradation is achieved through several parallel and subsequent steps, with each step having a certain consortium of active micro-organisms.

CARBOHYDRATES PROTEINS LIPIDS

SIMPLE SUGARS, AMINO ACIDS LCFA, ALCOHOLS

INTERMEDIARY PRODUCTS (VFA)

ACETATE HYDROGEN

METHANE NH

Hydrolysis Hydrolysis

Acidogenesis Acidogenesis

Acetogenesis Acetogenesis

Methanogenesis Methanogenesis

ORGANIC MATTER & WATER

BIOGAS (CH

+ CO

)

+ DIGESTATE BIO-FERTILIZER

Figure 4.1: Simplified anaerobic digestion of organic matter [Gujer, W., and Zehnder, A. J. B., 1983]

4.2 FACTORS AFFECTING THE ANAEROBIC DIGESTION PROCESS Temperature and pH

The bacterial growth in the digester is influenced by the temperature of the process. The higher the temperature, the higher the rate of microbial growth as well as the chemical and enzymatic reactions in the process until the optimal temperature is reached.

For the digestion of manure as a heterogeneous substrate, mesophilic and thermophilic processes are the most common according to the bacterial cultures required for the digestion of such materials.

The outdoor temperatures also affect the process. The gas quantity used will depend on the climatic

conditions outside. Also, in a very cold climate a bigger heat exchanger will be required to maintain the

process temperature and the heat losses will be much higher too. The optimum pH for the enzymatic

work is 6.0. This pH is maintained through the buffering capacity of the raw materials.

Carbon to nitrogen ratio (C/N ratio)

The C/N ratio indicates the comparative amounts of carbon and nitrogen present in the feed substrate. Nitrogen is an important nutrient for the development of bacteria in the process and will thus affect the yield of biogas. Therefore, a high C/N ratio would suggest a deficiency in nitrogen whereas a low C/N ratio would indicate the build-up of nitrogen in the system, an excess of which would form ammonia disturbing the pH stability of the system. An optimum C/N ratio of 20 – 30 is recommended for anaerobic digestion (Sadi, 2010).

Volatile fatty Acids (VFA)

The concentration on VFA formed in the intermediate processes affects the stability of the digestion process. Process instability will lead to the accumulation of VFA in the digester which may lead to a drop in pH value. VFA accumulation indicates either an organic overload or inhibition of the methanogenic bacterial culture due to the influence of other factors.

Ammonia

Proteins in the feed substrate are the main source of ammonia in the system. Ammonia is normally encountered in the system as a gas. High concentrations of this gas in the unionised form would inhibit the digestion process. The amount of ammonia would depend on the input substrate to the process.

Animal slurries are an example of substrate with a high amount of ammonia originating from urine.

[Teodorita A.S., 2008]

Inhibition and hydrogen partial pressure

The major inhibitor in the biogas process is the formation of ammonium-ammonia which is toxic for the active process bacteria. The rate of formation is directly proportional to the increase in temperature and pH. An accommodation time is required by the bacteria to get used to high concentrations of ammonia but the concentrations should increase step by step.

Other inhibitors for the process include oxygen, contaminants such as heavy metals, nitrates, sulphates, disinfective compounds, etc.

Technical and operational factors

Mixing: Mixing improves the contact between the substrate and the bacteria as well as a homogeneous mixture and constant temperature throughout the process. It also enables the release of biogas bubbles to the gas collection system. If not properly mixed, the production of biogas will be reduced and result in an unstabilised digestate. Foaming may also occur with insufficient mixing. Optimisation of mixing is important as mixers are often the most energy consuming components.

Hydraulic Retention Time (HRT): HRT represents the average time the raw materials spend in the biogas process which is given by the relation of reactor volume and the volume of daily feed [S. Luostarinen, A. Normak, M. Edström et al.; 2011]. The HRT depends on the source of raw material fed to the digester. For the digestion of manure, a HRT of 20-30 days is normally required. Kitchen wastes rich in starch containing vegetable residues will require a shorter HRT.

Organic Loading Rate (OLR): OLR describes the quantity of feed material to be treated to the process at a given time, that is, the amount of organic material (VS) in daily feed divided by the reactor volume [S.

Luostarinen, A. Normak, M. Edström et al; 2011]. All biogas processes have a threshold OLR above

which there are technical and microbiological limitations.

Feed Substrates to the digestion process

Basically most of all organic materials can be digested giving different yields of biogas depending on the carbohydrates, protein and fat contents. As far as agricultural manure and plant biomass are concerned, all can be fed to biogas plants. Food wastes and sewage sludge also are good inputs to the biogas plants.

Table 4.1: Theoretical biogas and methane production from carbohydrates, fats and proteins [Buswell

&Neave, 1930]

Substrate Biogas

(m ³ /t)

Methane (m ³ /t)

Methane content (%)

Carbohydrates 830 415 50.0

Fats 1444 1014 70.2

Proteins 793 504 63.6

Manure as a feed material to biogas plants

Manure is a good raw material for biogas plants for the following reasons:

 The production of manure is continuous and therefore continuously available

 manure contains all the nutrients required by the anaerobic bacteria, and

 it has high buffering capacity.

However, the high nitrogen content of poultry manure may require dilution with fresh or purified water or co-digestion with other less nitrogen-rich materials or some other specific technology in order to avoid inhibition by nitrogen.

Depending on the quantity and characteristics of the manure fed to the plant as well as the plant design, the manure can be either digested alone or co-digested with other raw materials. Different manure types will yield different amounts of methane depending on animal feeding and housing solutions, manure TS content and the bedding material used, among other factors.

The table below gives a summary of the different manure types and their biogas potentials.

Table 4.2: Average characteristics of different manures and their biological methane potentials (BMP) [1) Viljavuuspalvelu, 2004; 2) Steineck et al., 1999; 3) KTBL, 2010; 4) Ministerium für Ernährung, Landwirtschaft, Forsten und Fischerei Mecklenburg-Vorpommern, 2004; 5) Institut für Energetik und Umwelt et al.,2006; 6) Edström, 2011]

Manure TS

(%)

VS (% of TS)

Ntot (% of TS)

BMP (m ³ /tVS added)

BMP (m ³ /tFM added)

Ref.

Cow, liquid 5-14 75-85 3-6 120-300 10-20 1-5

Cow, solid 17-25 68-85 1.1-3.4 126-250 24-55 1-5

Pig, liquid 4-10 75-86 6-18 180-490 12-24 1-5

Pig, solid 20-34 75-81 2.4-5.2 162-270 33-39 1-5

Poultry, solid

32-65 63-80 3.1-5.4 150-300 42-156 1.3-6

4.3 ANAEROBIC DIGESTION SYSTEMS

There are various alternatives for the design of anaerobic digestion systems governed by the construction of the digester as well as the process technology. The type of system installation and the management of the plant dictate the efficiency of the latter. Simpler (single –stage) reactors, although easily designed, are less efficient and require constant monitoring. On the other hand, complex automated multi-stage systems are programmed to detect errors and send warning signals. These are more efficient although more costly [Luostarinen, Normak & Edström, 2011].

The engineering and planning for a particular digester will depend on several factors such as the scale of the plant as well as the raw material fed to the plant (biodegradability, VS & TS content), the quantity of input substrate, the simplicity desired, heat use, the intended use of the digestate (pasteurisation or not), local circumstances, economic factors (investment and operation costs) as well as the use of produced biogas.

Generally, agricultural biogas plants are categorised in to 3 scales by size:

 Household digesters (6 m ³ – 10m ³ capacity plants)

 Farm-scale plants (50 m ³ -5000m ³ )

 Centralised biogas plants (> 5000m ³ )

For the purpose of this project, we will focus on farm-scale biogas plants. These are classified into a further 3 categories depending on the capacities of the CHP units [Institut für Energetik und Umwelt et al., 2006]:

 Small scale ≤ 70 kW

 Medium scale 70–150 kW

 Large scale 150–500 kW

The small to medium scale would be applicable on single farms, while medium to large scale would most likely be of farm cooperatives.

Figure 4.2: General scheme of a common biogas plant with continuously stirred tank reactor (CSTR) in

Europe [Institut für Energetik und Umwelt et al., 2006]

Based on the data given above, for each individual farm, the rough technical design of the plant can be performed to calculate the following [Fischer T. and Krieg A., 2001]:

 Gas prognosis

 Digester size

 CHP size ( combined Heat and Power station – micro turbine/ gas engine size)

 Flow sheet

 Layout design

 Cost assessment

The next step would be to design the operation of the plant, also based of the data above [Fischer T.

and Krieg A., 2001]:

 Mesophilic or thermophilic process temperatures

 One or two- stage digestion process

 Type of mixing

 Mode of feed input

 Type of heat input

The results of this planning will determine which of the 3 major types of digesters will be most appropriate for that particular case.

4.4 PRE-TREATMENT STEPS

The initial treatment of substrate differs at different plants, depending on the material to be digested, as well as the final use of biogas and digestate produced. Sometimes more than one pre-treatment step is involved.

Milling/ crushing/ removal of grit and non-renewables

Blending of the manure with re-circulating sludge before the heat exchanger permits the manure to be heated before entering the digester.

Grinding or milling the input substrate decreases the size particle thus increasing the digestibility of waste that is hard to break down.

Thickening of materials with a small content of dry solids by for example, centrifuging.

Mixing of the digesting fluid permits a uniform fluid and constant temperature and prevents scum and grit accumulations.

Sanitisation

For material of animal origin, such as waste from a slaughterhouse, food waste and manure, digestion is preceded by a sanitation or hygienisation stage, which usually involves heating the material to 70°C for one hour (1774/2002/EC) or sterilisation (133 °C, 3 bar 20 min; 1774/2002/EC). This treatment ensures the elimination of pathogens and also loosens the bond structures resulting in more degradation and thus more biogas produced.

Start-up Inoculum

When a biogas reactor is started up, microorganisms from the inoculant need time to adjust to the

substrate that the specific biogas plant is going to treat. In a biogas plant, both the substrate and the

environment will differ from the original environment and it is important for the organisms to adapt to

enable a stable process. During this adjustment period, the organisms in the inoculant that are best able to survive in the new environment will grow and become established.

Microorganisms that are added via the new substrate may also play a role in the process. The more the environment from which the inoculant is taken differs from the environment in the digestion tank, the longer the start-up period will be. To achieve a quick and reliable start-up of the process, it is best if a microbial community is established already from the beginning, based on adaptation to a similar substrate. One way to achieve this is to start the process using digestion tank contents from an already operating process that uses a similar substrate.

4.5 BENEFITS OF BIOGAS

Biogas production by anaerobic digestion clearly have the following benefits for owners / operators:

Figure 4.3: Benefits of Biogas from the anaerobic digestion of organic wastes 4.6 POTENTIAL ENERGY USES OF BIOGAS

Direct combustion of the biogas is still the most energy efficient option. The biogas can be directly used for cooking, heating, cleaning, drying and hot water. The biogas generated will sufficiently reduce the regular consumption of other cooking fuels such as LPG.

Biogas can also be used to generate electricity using selected technologies (through the Otto or diesel engines, (both internal combustion engines). Before the feeding of biogas to generation sets, the gas has to be passed through a gas scrubber to remove unwanted particles, gases, moisture etc. In the diesel engine, commonly known as the dual fuel engine, diesel or another oil-based fuel is used for the ignition of the turbine as the heat of compression of biogas is not sufficient for the ignition of the engine. In the Otto gas engine, only biogas is used as fuel. They have spark plugs for ignition and a

Biogas

Great potential for use of various waste streams

thus avoiding treatment

costs Cooking fuel

Suitable for stand alone decentralised

farms

Production of heat and electricity An

appropriate technology to exploit energy potential from wet organic

waste Sustainable

raw material for chemicals Alternative

fuel for vehicles Versatile energy carrier

Decreased dependency

on natural gas

imports

gas/air mixing system for providing a combustible mixture to the engine. Otto engines are designed using a lean burn technology, including turbocharger, with a surplus of air for improving efficiency and reducing emissions. The externally fired gas turbine is a novel technology under development for small and medium scale heat and power supply systems.

In the northern part of the Europe, for example, in Sweden or Germany, biogas is also used as a vehicle fuel and can be distributed to the public natural gas network, after upgrading the biogas.

Figures show that the number of vehicles using biogas as fuel in Sweden in 2010 was 30 100 cars, 1 400 buses and 500 trucks [Energigas Sverige, 2011]. This biogas is from the anaerobic digestion at wastewater treatment plants or from biogas plants using food wastes as feed substrate.

In a more innovative technology approach, energy from the biogas can be stored in fuel cells by passing the biogas through a reformer upstream.

ANAEROBIC DIGESTER MANURE/

FOOD AND AMENITY WASTE BIOMETHANE

DIGESTATE

COOKING GAS

ELECTRICITY

VEHICLE FUEL

HEATING

BIOGAS

Figure 4.4: Potential uses of biogas and digestate from anaerobic digestion 4.7 THE DIGESTED RESIDUAL PRODUCT (BIO-MANURE)

The by-products of the anaerobic digestion process are the solid and liquid bio-fertilisers, which

normally come out as a slurry. This slurry can be applied to the arable land as it is by using a special

slurry tanker as shown in the plate below.

The slurry can also be separated into solid and liquid fertilisers using different processes such as centrifugation. But for small and medium digesters, this is not economically viable as such processes are quite complicated and costly. The solid fertilizer could be packed and eventually sold to the public so that the beneficiary could recover a part of the project costs.

4.8 HOW BIOGAS IS USED IN MAURITIUS AT PRESENT

Example 1: Biogas Production for the Ecological and Economic Treatment of Cattle Waste

Bio-digesting is a technology which has not taken off within the community of farmers in Mauritius.

But some attempts have been made for its adoption with the support of UNDP-GEF small grants programme and it seems to be quite a success.

The project comprised of the installation of infrastructure for a pollution-free environment as well as an economical system of milk production through the setting up of digesters for the treatment of animal waste generated by the breeding activity of 13 farmers who are members of the Livestock Keepers Association. Each farmer owns around 6-7 cows as a small backyard farm at their residence generating about 876 tons of manure per year thus producing about 129000 cubic metres of biogas per year, or 217 kg of gas per day capable of replacing four units of 12 kg LPG bottles per month (as stated by one of the families benefitting from this project). The environment also benefitted from this project as it represents a carbon dioxide emissions reduction of 530 tons. [Biogas Production for the Ecological and Economic Treatment of Cattle Waste; http://sgp.undp.org/]

This project promoted the use of renewable energy and improved the living conditions of rural animal keepers by ensuring a cleaner and more hygienic environment, while at the same time encouraging the use of natural methods for agriculture through treatment of animal waste for use as fertilizer. The animal waste will be washed and directed into a digester, which will treat the wastes to produce biogas energy for cooking and water-heating purposes. The effluents from the digester will be used as fertiliser and for irrigation of the fields where fodder and other crops will be grown.

Example 2: St Martin Municipal Wastewater Treatment Plant

The St Martin Wastewater Treatment Plant treats 70,000 cubic metres of wastewater per day through the anaerobic direction of the wastewater. The plant is operated by the German company. Berlinwasser International AG. The biogas produced during the digestion of the sludge (feed of 250-280 m ³ /day, of solid content of about 25% and Volatile Solids content of about 70%) is converted into electrical energy which is then used for the operation of the plant. The biogas production yield is typically 2500- 2600 Nm ³ /day. 25% of the electricity needs is provided from the biogas produced, using a combined heat and power plant [Roumeela Mohee & Acknez mudhoo, 2006].

Example 3: Mare Chicose landfill, Mauritius

Two spark ignition engines of 1MW and 2 MW are installed at the landfill site use biogas, namely

methane from the anaerobic digestion of wastes from the landfill to generate green electricity to be

used in the office and for the leachate treatment as well as provide electricity to the village of Mare

Chicose, representing some 20,000 households. This project converts energy from a source that was

previously thought of as waste. It is estimated that the peak generation of biogas from the landfill will

be around 2013 to 2015. The digestate produced can be used as cover material in the landfill cells.

5 EXPERIMENT SETUP 5.1 AIM OF THE EXPERIMENT

The aim of the on-campus experiment is to determine the amount of biogas that can be obtained from food wastes, the logistics behind and to be able to use the biogas in the Heat and Power Laboratory.

5.2 AMOUNT OF WASTES TO BE DIGESTED

A survey of available wastes was performed in the three (3) restaurants in the vicinity of the KTH University. The three restaurants in the survey were the ‘Brazilia restaurant’, the ‘Restaurant Q’, the

‘Restaurant Sisters n Bro’. The results of the survey are shown in the Table 7.1 below.

Table 5.1: Survey of restaurant wastes

Question Restaurant Brazilia Restaurant Q Restaurant Sisters n Bro*

How much raw/

cooked organic wastes does the restaurant generate per day?

The wastes are not segregated. But at least 2 big bags of wastes weighing approximately 25 kg each are thrown to the trash bin every day, mostly composed of organic wastes for around 300 to 350 servings per day.

The restaurant is already in a recycling programme. So the wastes from the dishes are collected by biogas producing company.

Also, there are no raw wastes produced at the restaurant as the raw vegetables and meat are delivered already processed.

They produce as much as 2 big bags of kitchen and restaurant wastes per day, also representing 40-50 kg per day for around 450 servings.

*The restaurant management later stated that it has started a recycling programme and would not be able to supply the wastes for the experiment

What is being done with the used oil/fat?

The used oil is sent for recycling

The used oil is sent for recycling

The used oil is sent for recycling

Therefore, we can assume that we will have around 40-50 kg/ day of restaurant wastes from the Restaurant Brazilia for the experimental biogas plant setup.

5.3 DESIGN AND SIZING OF THE BIOGAS PLANT

Before designing and setting up the digester there are important factors to consider:

 Amount of biogas/ amount of input material – is it a good substrate?

 Gas quality

 Temperature control (process is temperature sensitive, the temperature should be quite stable during the digestion process)

 Operating parameters

 One or two stages of digestion

 Continuous or batch process

 Choice of materials for the digester and auxiliaries

 Leakage control (leakage of biogas from the process or gas storage is dangerous and is a strong greenhouse gas.

 Sanitisation: depends on substrate and use of digestate, as well as prevailing regulations

 Permissions required for setting up of plant: permissions for spreading of manure as well as

permissions for the location of plant as there are boundaries and buffer areas to be respected

The following biogas plant design and sizing is based on the generation of 100 kg of restaurant wastes per day.

Calculation of the reactor volume:

There are two ways of getting to a first estimate of the size of the digester - organic loading rate and hydraulic retention time (HRT).

As a rule of thumb, the Organic Loading Rate should be about 3.5kg VS/m ³ of reactor Assuming federate : 100kg of fresh (raw) feedstock per day

Given TS% : 20% (% Dry Matter Content per wet weight (DMC/wet weight))

TS : 20 kg

Given VS% : 90% of TS (Volatile Solid per kg of Dry Matter (VS/kg DM))

VS : 18 kg

If 3.5kg VS requires : 1 m ³ of reactor volume Then 18 kg VS : 5 m ³ effective volume Reactor volume required = 5.0 m ³

Or

Assuming 22 days of HRT at thermophilic temperature of 55°C

Input substrate : 100 kg of raw kitchen waste + ~100 litres of water (to bring the VS% down to 10% of total mass of input substrate)

: 200 litres

Volume of reactor : 22 x 200 litres =4.4 m ³ Applying a safety factor of 10%:

Reactor volume required = 5.0 m ³

Design of plant:

The plant design is based on several factors:

 The amount of wastes

 The cost of equipment installation and running of the plant (considering that Mauritian farmers do not have the facility to implement a ‘state-of-the-art’ plant.).

The plant should be able to be stand alone, that is, suitable for de-centralised locations, as would be the case of most farms in Mauritius. The plant should be able to be easily operated, so that a farmer can operate the plant without requiring any particular skills.

Option 1: Do-it-yourself (DIY) biogas plant

There are several designs of easy DIY plants for small scale plants, usually backyard or domestic biogas plants. The highlights of this design include:

 Flexibility to be used for either continuous flow or plug-flow processes.

 The small compact design requires a small site area

 Inexpensive design materials. Bladder made of inexpensive tarpaulin can be used, which is tougher,

more durable and safer than polyethylene(PE) for example.

 Clean and sanitary

 Versatile: By raising the top section of the bladder, a suction (vacuum) effect may be created to extract gas. Conversely, by pressing down or applying weight on the top of the bladder, gas pressure is increased or adjusted.

 Simple to operate and functional.

Examples of some DIY plants are shown below:

Figure 5.1: Philippine BioDigester by: Gerardo P. Baron, December 2004, (Tarlac City, Philippines)

[http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm]

Figure 5.2: Completed PE digester prior to final installation of lid and wrapping with insulation

[http://biorealis.com]

Option 2: Low-cost available ready-made digesters

Figure 5.3: Small and medium scale digester biogas plants, by BioTech, India [http://www.biotech- india.org]

These digesters are made of fibreglass lined polyvinylchloride (PVC) material which is relatively cheap and impervious to methane gas. The image to the right shows the biogas plant complete with upgrading equipment and CHP. The cost of installation is slightly on the high side but the operation is simple and economically beneficial.

Option 3: Containerised biogas plant

The advantages of this type of plant are that it is transportable from one site to another. All the components are integrated in the system. The plant is very compact and does not require much land area. The commercialised containerised plants are manufactured according to international standards concerning the gas storage tank as well as safety of the equipment.

Figure 5.4: Containerised biogas plant by BioBowser, Australia [http://www.srela.com.au/biobowser.php]

This biogas plant is also complete with the waste processing tank and crusher as well as the upgrading

unit as shown in the figure below.

Figure 5.5: Components of the BioBowser containerised biogas plant [http://www.srela.com.au/biobowser.php]

Substrates to the JTI mobile biogas plant include, but are not restricted to:

• Sewage sludge

• sludge from grease

• Various waste products from food industry

• Sorted food waste

• Slaughterhouse residues

• Sludge from pulp

• Slurry

• Plant Residues

• Energy crops

Possible process testing with the JTI mobile biogas plant include:

• Co-digestion with the new substrate

• Digestion at higher TS and higher biological load

• Evaluate two-stage anaerobic digestion

• Test the effect of different retention times

• Mesophilic v.s. thermophilic digestion

• Sanitation by thermophilic digestion v.s. pasteurization

• Studies of digestate qualifying small

• Component Tests at different process conditions

• Try on biogas production at plants that are not currently producing biogas

• Demonstration and training

Figure 5.6: The Research biogas production unit at JTI, Swedish Institute of Agricultural and Environmental Engineering

5.4 CHOICE OF BIOGAS PLANT AND JUSTIFICATIONS

 The do-it-yourself option was not chosen on the basis of the high equipment and material standard requirements in Sweden as well as the requirements of safety of the handling of explosive material on campus.

 BioTech India sent a quotation for the treatment of 100 kg of restaurant wastes by proposing a 5 m ³ digester including the biogas generation system, pre digester, slurry loop system at an equipment cost price of EUR 12 450, without costs of transportation or installation. But the main problem was the delivery time of the equipment which was 60 days as from manufacture to delivery at local port. They were also reluctant to give additional information on the plant proposed.

 BioBowser would have been the most interesting technical choice, but the price would have been even higher than the Indian technology.

 The JTI containerised unit is available for rental for the months of May and June and is a viable option for the on-campus experiment set up. The plant has already obtained the certifications for the gas storage tank and the approvals from the fire departments for previous research projects.

By elimination, the JTI biogas plant was chosen.

5.5 LOGISTICS: PLANNING THE BIOGAS PLANT Feedstock:

According to the Researcher at JTI, Mr Gustav Rogstrand, an average of 80kg per day of wastes would be required tofeed the plant for the process to run correctly. For a 2-week running period, the collection of the wastes should be started 2 weeks prior to the start-up of the plant. The waste has to be covered to avoid rodents and birds invasion.

Gas volume produced

The gas produced, according to Gustav, would be 6-10m ³ /day. A 200-litre gas storage balloon tank

would be supplied with the equipment but another tank for transportation of biogas for use in the

laboratory would be required.

A certified gas storage balloon tank of 500 litres on the market is around EUR 620 (Schanflex APS, Denmark) [http://www.schanflex.dk].

Site requirements and preparation:

Surface area

The require surface area would include space for the containerised digester, 8ft container for the grinder, area for the gas storage tank (placed in trailer) as well as a buffer zone of 2 metres around the plant. The site should also respect the required 10 metres from any building structure recommended by the Fire Department. The area should be a flat levelled surface so that the weight sensors in the tanks would give the correct data.

Surrounding environment

The area should be fenced with limited access to authorised persons only. For safety reasons, the area around the flaring equipment should be clear. The branches around the mobile plant had to be cut.

Electricity access points/ Power supply available

One 63A outlet and one 32A outlet within a reasonable distance from the mobile plant would be required for the running of the plant as well as a 16A outlet for the grinder equipment. But as long as the grinder is not running simultaneously with the motors and pumps, the 32A outlet can be used.

Water access

Access to water is essential for the preparation of the feedstock to the plant and to ensure a clean site at all times.

Disposal/ use of digestate

About 250 litres of digestate will be removed from the digester each day. This digestate is too much to be added to the yard composting piles at this time of the year. Therefore, the digestate will be carted away by registered sewage carriers every 2-4 days.

Odour control

The collection of wastes will start 2 weeks before the start of operations. The wastes will be kept in covered bins. The site should be at a reasonable distance from buildings to prevent any odour inconveniences. Nevertheless, notices have been put at the site as well as at the entrances of the nearest buildings.

Personal Protective Equipment

All necessary PPE for the handling of wastes and biogas would be provided.

Approval from local authorities Facilities Management

A meeting was held with the facilities management (Mr Göran Holmberg , Akademiska Hus) to get

approval for the proposed site which is the compost site of the KTH university. The site was chosen

as it fits all the above requirements. They would clear the site before the delivery of equipment. They

will also supply electricity and water at the site.

Figure 5.7: Proposed site for the biogas plant setup Fire department

The Fire department was contacted and briefed about the project. They required a full application for the handling of flammable materials. This type of application generally takes 3 weeks to be processed.

5.6 EQUIPMENT SETUP

The JTI mobile biogas plant main components

The table below shows the functions and capacities of the main components of the mobile biogas unit.

Table 5.2: Mobile biogas plant basic data (Source: JTI)

Function Capacity

Digester volume 5 m ³ (6 m ³ total incl gas volume) Processing temperature 30 - 70 °C

Residence time 10 - 50 days

Process capacity 100 - 500 kg wet weight/ day, 0.5 to 25 Nm ³ of biogas/ day (65/35) Hygienisation capacity 50-600 kg / round (pasteurization - max 80 °C)

Decomposition Selectable (on board or external) Heating system Electric boiler on board 26 kW

Valve Drive Automatic compressor on board

Emergency gas treatment Gas monitoring unit and automated flare on board Gas volume measurement Continuous online flow rate measurement

Gas quality measurement Continuous online - CH 4 , CO 2 , O 2 and H 2 S

PLC Management Fully automatic with remote management and logging via 3G Training

Training on the operation of the plant was provided by JTI as well as what to do in case of alarm or dysfunction of the equipment or process. Safety procedures were also provided.

Inoculum

Inoculum could be obtained at any running active bio-digester, but preferably if food wastes would be digested, inoculum from a similar plant running under same conditions would be best, else any wastewater treatment plant using the anaerobic digestion process would do. The amount of inoculum should be equal to the reactor volume of the proposed digester.

Collection and storage of raw material (restaurant/ kitchen wastes)

The restaurant does not segregate its wastes. The waste was collected twice per week using a mobile bin (on wheels). The waste was stored in large covered bins at the experiment site before the organic part could be separated and fed to the digester.

However, it was observed that the waste collected from the restaurants over the first two weeks were not usable. Therefore, food waste was provided by a waste management company, RagnSells, who own digesters themselves. The waste was delivered in a two-tonne container. The wastes are food wastes from a supermarket and had to be separated from plastic containment. The inorganic part was kept in a separate bin for collection by registered waste carrier.

Feeding new substrate to the digester

The feedstock would be fed to the grinder using a bucket to the top board, which is then scraped using a rubber-pallet knife. When the grinder is switched on,

water will be added to the feedstock at a desired flowrate to reach the required dilution to 10% DMC prior to being pumped to the buffer tank.

The Disperator® grinder has a metallic feeding table to prevent any metallic objects such as a fork can enter the grinder. The machine grinds all kitchen wastes including bones. The only kitchen waste that should not be fed to the grinder, as per supplier’s recommendations, is fish-skin for its rubber-ish and

slippery properties. Figure 5.9: Disperator® grinder

The first feed was done on Tuesday 5 ^th June 2012. It took 29 minutes to feed the biogas unit (reception tank) with 139.2 kg waste and 85.65 litres of water. The grinder was set to mix the waste with 3 litres of water per minute. Later that same day, a second batch of waste was grinded. The grinder was set to mix the waste with 2 litres of water per minute. It took 4 minutes to feed the reception tank with 35.6 kg waste and 8 litres of water.

A second feed was prepared on Tuesday 19 ^th June 2012. The grinder was run for a period of 22 minutes. During that time 131.8 kg of waste consisting mainly of bread went through the grinder with a water mix of 42.86 litres.

Total amount of feed slurry during the experiment = 450 kg of feed substrate Day-to day operation

Table 5.3: Operation of the biogas plant

SN Description Frequency Responsibility

1 Fill the digester with inoculum (provided by a digestion plant in Uppsala treating 100% food wastes at the same thermophilic conditions so that the inoculum will quickly adjust to the new substrate environment).

First day of operation KTH – rental of a sewage truck

2 The inoculum is heated to a constant temperature of 55°C

First day of operation JTI/ Operator 3 Fill the space above digestate in the digester

with nitrogen to ensure anaerobic conditions during the process (displacing any oxygen that could be present)

First day of operation JTI/ Operator

4 Run a process to understand the procedure (part of training)

Every day or 2 times daily ensuring an interval of at least 10 hours between the loadings

Operator

5 Separate organic wastes from other wastes, if necessary

Every four days Operator

6 Test a sample of raw waste to find VS and DS content to find the appropriate loading rate

Once at early stage 7 Cut wastes to a size to fit the entrance slot of

the grinder

Weigh the wastes before feeding the grinder, where water is added to form a slurry which is pumped to the buffer tank

Every four days Operator

8 Test for DMC and VS of the input slurry to ensure proper dilution

Every four days Operator

9 Sampling of digestate to test for pH, ammonium ammonia, VS, TS, DMC, VFA

As and when necessary Operator 10 Ensure disposal of digestate by registered

sewage truck

Every 2 to 4 days, or as and when necessary

Operator 11 Take daily readings from the software to

ensure proper processing conditions are respected.

At least once daily Operator

12 Emergency shutdown of the flaring equipment in case of thunderstorm (the equipment works with static electricity). This cannot be done on

When alarm is activated or

when forecasted

thunderstorms.

Standby-operator

5.7 RESULTS AND DISCUSSIONS

The analysis of the input slurry, after grinding and addition of water gave the following results:

Table 5.4: Results of analysis of feed substrate (sample taken on the 13 ^th June 2012) Parameter Result

pH 6.85

TS (%) 11.19 VS (%) 10.41 NH4-N (g/L) 0.47

If 3.5kg VS requires = 1 m ³ of reactor volume

Then 5 m ³ of reactor volume = 3.5 x 5 = 17.5 kg of VS From the analysis of feed substrate, VS% = 10.41%

First day feed = 139.2 + 35.6 = 174.8 kg of feed substrate Total VS fed = 10.41% x 174.8 = 18.2 kg of VS

This shows that the feed substrate consistency was a bit high on VS content. This allows for more water to be added to the raw waste. A water mix of 3 litres per minute to the grinder was appropriate to bring the volatile solids content to about 3.5 kg per cubic metre of reactor volume.

The amount of feed to the reactor was programmed and recorded throughout the experiment. The amount of biogas produced was also recorded throughout. The gas produced was sampled at regular intervals and analysed to note the quality of gas produced (%carbon dioxide and %methane). The graphs below show the results obtained from the experiment.

Figure 5.10 : Amount of biogas produced as a percentage of gas storage bag volume 0

10 20 30 40 50 60 70 80 90 100

Dat e /tim e 20 12 /0 6 /0 4 21 :17 20 12/0 6 /05 03 :5 7 20 12/0 6 /05 11 :4 9 20 12/0 6 /06 00 :5 4 20 12/0 6 /06 13 :5 9 20 12/0 6 /07 03 :0 4 20 12/0 6 /07 16 :0 9 20 12/0 6 /08 05 :1 4 20 12/0 6 /08 18 :1 9 20 12/0 6 /09 07 :2 4 20 12/0 6 /09 20 :2 9 20 12/0 6 /10 09 :3 4 20 12/0 6 /10 22 :3 9 20 12/0 6 /11 11 :4 4 20 12 /0 6 /1 2 00 :49 20 12/0 6 /12 13 :5 4 20 12/0 6 /13 02 :5 9 20 12/0 6 /13 16 :0 4 20 12/0 6 /14 05 :0 9 20 12/0 6 /14 18 :1 4 20 12/0 6 /15 07 :1 9 20 12/0 6 /15 20 :2 4 20 12/0 6 /16 09 :2 9 20 12/0 6 /16 22 :3 4 20 12/0 6 /17 11 :3 9 20 12/0 6 /18 00 :4 4 20 12/0 6 /18 13 :4 9 20 12/0 6 /19 02 :5 4 20 12 /0 6 /1 9 15 :59 20 12/0 6 /20 05 :0 4 20 12/0 6 /20 18 :0 9

BIOGAS PRODUCED AS A PERCENTAGE OF

0.6M ³ GAS STORAGE BAG